Engine detonation control by acoustic vibratory member



Oct. 26, 1954 A. G. BODINE, JR 2,692,590

ENGINE DETONATION CONTROL BY ACOUSTIC VIBRATORY MEMBER Filed Sept. 26, 1951 flmp. (1 Phase Shift Feed Baez IN V EN TOR.

14L 8521' G. Boo/NE J12.

Patented Oct. 26, 1954 ENGINE DETONATION CONTROL BY ACOUSTIC VIBRATORY IJEMBER Albert G. Bodine, Jr., Van Nuys, Calif. Application September 26, 1951, Serial No. 248,421

9 Claims. 1

This invention relates generally to internal combustion engines, and to means for suppressing irregular burning and detonation of fuel-air mixture therein. The invention is based on my discovery that detonation in combustion involves acoustic phenomena and can be alleviated by use of certain acoustic apparatus used in combination with the combustion chamber.

The present application is a continuation-inpart of my prior application entitled Method and Means for Suppressirr Detonation in Internal Combustion Engines, filed July 14, 1947, Serial No. 760,914, and allowed January 24, 1951, now abandoned. Reference is also made to my generic application entitled Engine Detonation Control by Acoustic Methods and Apparatus, filed as a continuation-impart of Serial No. 760,014 on July 2, 1951, Serial No. 234,688, new Patent No. 2,573,536, wherein some of the subject matter of the present case is disclosed. For a full description of the acoustic aspect of detonation in combustion, and my basic acoustic solution for controlling detonation in combustion, reference is made to my said Patent No. 2,573,536.

The object of the invention is the provision simple and efiective acoustic means for con trolling detonation in combustion, following the basic teachings of my aforesaid prior applications.

Only briefly stated herein, the present inven tion is based on the fact that detonation in an engine combustion chamber produces sound Waves, a large part of which rise to high ampli tude at resonant frequencies of the chamber, and that these sound waves produce the various harmful manifestations of detonation. Accordingto my basic invention, I curtail or inhibit these harmful efiects by interfering with or at tenuating the detonation induced sound waves, and this is done by use in connection with the combustion chamber of acoustic attenuation means made responsive to the frequencies at which the detonation induced sound waves build up to high amplitudes.

The, present invention, broadly speaking, pro-- vides in the combustion chamber a vibratory member having a surface exposed to the interior of the chamber, and arranged to vibrate at a resonant frequency of the chamber, at which detonation induced sound waves rise to peal: esonant amplitudes. According to one specific and preferred arrangement, this vibratory member is in the nature of an elastic diaphragm which closes the mouth of a resonant absorber, e. g., a Helmholtz resonator, which otherwise opens unrestrictedly into the combustion chamber. This resonator-diaphragm combination is tuned to be responsive to a resonant frequency of the chamber, at which detonation induced sound waves become greatly amplified and reach high energy levels. The device is in effect a resonant absorber, and attenuates the resonant sound wave peaks by energy absorption and dissipation. Other variations will appear in the following specification.

The invention will be best understood by referring now to the following detailed description of certain present illustrative embodiments thereof, reference for this purpose being had to the accompanying drawings in which:

Figure 1 is a vertical sectional view of an internal combustion engine of the piston type employing two different forms of the invention; and

Figure 2 is a vertical fragmentary section of the combustion chamber of an engine, showing a modified form of the invention.

In Figure is shown an L-head engine com-- prised of a water cooled head ll secured to block 50, a piston 52 reciprocable in cylinder it in block it an exhaust valve i l, and a spark. plug i5. It will be understood that, as in conventional L-head engines, an intake valve (not shown) will be located. alongside exhaust valve it, such valve being of course out of the plane of the drawing. Block I 0 and head l have cooling jackets it and I! respectively, and head H has an inner COillbustion chamber wall which encloses a combustion chamber space 19 over the cylinder and valves, as shown.

One or more of the combustion chamber walls, here the head wall i8, is provided with acoustic Wave attenuation means responsive to detonation induced sound wave patterns in the combustion chamber. As here shown, the wall 18 is formed with one or more, preferably a plurality, of acoustic resonant absorbers 2b, in this instance in the nature of Eelmholtz resonators-together with thin flexible or elastic vibratory plates or diaphragms 2! which separate the mouths of resonators from the combustion chamber. These vibratory diaphragins 2! are fastened to the wall !8 in any suitable manner, such as by welding. The dimensions of the resonant absorbers 29-? l, including the size of the cavities, and the thicknesses of the diaphragms, are made such that the absorbers are resonant to the frequency or frequencies at which high amplitude detonation induced vibrations tend to occur within the com bustion, chamber. These frequencies are found to be resonant frequencies of the combustion chamber. If such high amplitude detonation vibrations are found at more than one frequency, the resonators may be of different dimensions to correspond with the different frequencies encountered. Ordinarily, the detonation vibrations in the combustion chamber will occur at well defined frequencies, corresponding with different resonant modes of the chamber, though there is likely to be some frequency spread, and the resnators are designed, in accordance with known acoustic practice, to correspond with or be responsive to the full width of the frequency band or bands within which detonation vibrations in the chamber rise to troublesome amplitude. Also, while I have here shown Helmholtz type resonators, this is merely illustrative, since the quarter-Wave pipe type of resonator will serve as well and is a known equivalent, as explained in my aforesaid application Serial No. 234,588.

The resonant absorbers as thus described absorb energy from the sound waves created in the combustion chamber upon onset of detonation, and very substantially attenuate the detonation wave pattern. Without the high amplitude detonation wave pattern, at a resonant frequency of the combustion chamber, the usual harmful manifestations of detonation do not appear.

The energy of the detonation wave pattern is absorbed partly by the Helmholtz resonator cavity, and partly by the vibratory diaphragm or plate which separates the interior of the cavity from the combustion chamber. It will of course be understood that while the diaphragm separates the resonator cavity from the combustion chamber, it does not stand in the way of sound wave transmission. In the preferred practice of the invention, the vibratory diaphragm is tuned, in combination with the cavity in back of it, to be resonant to the detonation frequency of the combustion chamber. The vibration amplitude of the diaphragm, assuming such tuning, becomes substantial, and a substantial amount of the acoustic energy of the detonation induced sound wave may thus be absorbed, and the detonation Wave reduced accordingly. It will be seen that the resonator cavity absorbs a part of the acoustic energy of the detonation wave, and that the vibratory plate absorbs another part of the acoustic energy. The latter effect is over and above that owing to the cavity behind the diaphragm. The diaphragm also serves the important function of preventing carbon deposit Within the cavity, and this benefit is of course independent of energy absorption by the diaphragm, so that in this as pect, tuning of the diaghragm, and its elastic character, are not important, so long as it permits the cavity to resonate. Moreover, in cases where the diaphragm has but small elasticity or stiffness, its stiffness efiect on the resonant frequency of the combination is not dominant, and it is sufficient merely to tune the cavity to resonance, taking into account only the inertia of the diaphragm, and disregarding its tuning. It should also be mentioned that the vibratory plate or diaphragm may be used without a resonant cavity behind it. In such case, there may be a cavity behind the diaphragm, not tuned to be resonant, or the space behind the diaphragm may open to atmosphere, or to the water jacket. It is important in all cases, however, that the diaphragm resonator as a whole be tuned to establish resonant responsiveness to the frequency of the detonation wave pattern tending to be created in the combustion chamber.

Figure 2 shows an alternative embodiment,

wherein an engine head 30 has its combustion chamber wall 3! formed with one or more apertures 32 closed by vibratory elastic plates or diaphragms 33, the latter having bonded to its back surface a layer or body 34 of material having substantial internal friction. The material making up the layer as may, for example, consist of sintered powdered metal, suitably bonded to the plate 33. Such material, upon vibratory bending of its supporting plate 38, creates substantial internal mechanical friction as a result of its responsive flexing, and this internal mechanical friction is absorptive of substantial vibrational energy.

The thickness of the diaphragm 34 is predetermined to give an elastic stiffness which, in combination with the stiffness and mass inertia of the backing layer as, and with the reactance of the water in the engine jacket 38, will cause the diaphragm to respond to the frequency of the detonation induced sound waves in the combustion chamber.

Thus, in operation, the diaphragm 33 vibrates responsively to detonation induced sound wave patterns within the combustion chamber, and energy is absorbed from the detonation sound wave by reason of the internal friction resulting from bending of the plate 322 and particularly of the sintered powdered metal backing layer 3 8-.

Figure 1 shows also an alternative sound wave attenuation means, wherein a vibratory surface, analogous to that presented by the inner face of the aforementioned diaphragm type of attenuator, is driven by a sound wave generating device so as to oppose the detonation induced sound waves and attenuate them by mutual opposition or cancellation. Reaching into combustion chamber I9 is a vibration pick-up device 46 of any desired type capable of producing an electrical current at its output terminals in response to sound waves reaching a high impedance refleeting surface of the combustion chamber. The terminals of pick-up 48 are connected by leads ll to an amplifier and adjustable phase shifter 52, adjusted to produce an amplified output current whose phase is shifted from the phase of the input current flowing in leads 4i. Output leads 43 connected to amplifier and phase shifter 42 go to the coil l surrounding a magnetostriction bar 45 mounted in a casing at which is inserted in head I l adjacent pick-up 40. The inner end surface M of magnetostriction bar 35 is approximately in the plane of the surface of the combustion chamber, and is near pick-up til. Magnetostriction bar 35 is mounted near its mid section, so that its two oppositely projecting end portions alternately elongate and contract in step With the electrical current fed to coil 46.

The electrical current fed to coil it having its phase properly shifted with relation to that delivered by pick-up 50, the motions of the ends of pick-up 40 and magnetostriction bar ll may be adjusted to be out of phase. The end surface of bar All becomes a source of sound waves, which are 180 out of phase with the pick-up attenuating detonation waves received at the surrounding combustion chamber surfaces, and the two waves, thus 180 out of phase, have a neutralizing effect on one another, so that the original detonation wave is attenuated.

In a modification, the amplifier 32 is designed to oscillate at some frequency other than detonation frequency, thus forcibly maintaining a particular wave pattern to control combustion rate and prevent severe detonation. Pick-up 40 and connections 4| can be used to trigger the oscillations of amplifier 42; or if desired, pick-up 40 may be eliminated and amplifier 42 made to oscillate by conventional circuit arrangements with the trigger means.

It will be understood that the drawings and descriptions are illustrative only and not restrictive on the broad invention, and that various changes in design, structure and arrangement may be made without departing from the spirit and scope of the appended claims.

I claim:

1. In an internal combustion engine, the cmbination of: a substantially rigid walled resonant combustion chamber, and acoustic wave attenuation means closely acoustically coupled with said combustion chamber and having frequency respons for a characteristic frequency band of sound waves generated in said resonant combustion chamber by detonation, said acoustic wave attenuation means being located externally of the interior wall surfaces of the combustion chamber Wall, and there being a continuous sound wave transmission path between said wave attenuation means and the interior of said combustion chamber, said attenuation means including a vibratory diaphragm across said wave transmission path and in unrestricted communication with said detonation generated sound waves, said vibratory diaphragm being tuned to have a resonant response for said characteristic detona tion-generated frequency band, all in such manner as to afford a close acoustic coupling for the detonation frequency band, with resulting substantial reduction in the amplitude of the detonation sound waves occurring within the combustion chamber.

2. In an internal combustion engine, the combination of a substantially rigid walled resonant combustion chamber, and acoustic wave attenuation means closely acoustically coupled with said combustion chamber and having frequency response for a characteristic frequency band of sound waves generated in said resonant combustion chamber by detonation, said acoustic wave attenuation means comprising a perforation through the combustion chamber wall, and a vibratory diaphragm closing said perforation, said vibratory diaphragm being tuned to have a resonant response for said characteristic detonationgenerated frequency band, all in such manner as to afford a close acoustic coupling for the detonation frequency band, with resulting substantial reduction in the amplitude of the detonation sound waves occurring within the combustion chamber.

3. A combustion chamber having a substantially rigid defining wall providing a surface adapted to reflect sound waves originating within the combustion chamber, there being a plurality of acoustic wave attenuation cavities sunk into said wall from said surface, said acoustic cavities being tuned to be resonant to a detonation sound wave frequency band desired to be eliminated,

and vibratory plates separating said combustion chamber from said acoustic cavities.

4. A combustion chamber for an internal combustion engine, having, in combination, a combustion chamber wall having a surface adapted to reflect sound waves originating within the combustion chamber, a resonant absorber cavity arranged in said wall in the region of said surface with its mouth in acoustic communication with said chamber, and a vibratory diaphragm extending across and closing said mouth, one surface of said diaphragm being in unrestricted communication with the interior of said combustion chamber said cavity and diaphragm being tuned to be resonant to a detonation sound frequency band desired to be eliminated whereby to afford a close acoustic coupling to the combustion chamber within said detonation frequency band.

5. A combustion chamber having a substantially rigid defining wall providing a surface of high acoustic impedance adapted to reflect sound waves originating within the combustion chamber, ther being perforations through said wall providing regions of low acoustic impedance, and vibratory plates closing said perforations.

6. The subject matter of claim 5, including an energy-absorbing body of high internal friction mounted on said diaphragm.

'7. The subject matter of claim 6, wherein said energy absorbing body is composed of sintered powdered metal.

8. In an internal combustion engine, the combination of: a substantially rigid walled resonant combustion chamber, and acoustic wave attenuation means operatively combined with said combustion chamber and having frequency response for a characteristic frequency pattern of sound waves generated in said resonant combustion chamber by detonation, said wave attenuation means being arranged in sound wave transmissive communication with the sound waves in said chamber and comprising a vibration pick-up adapted to produce an electric current responsive to sound Waves received thereby, a means for shifting the phase of said current, and sound wave generating means actuated by the phaseshifted current, all in such manner as to effect substantial reduction in the amplitude of the detonation sound waves occurring within the combustion chamber.

9. A combustion chamber having a substantially rigid defining wall providing a high impadance reflecting surface for detonation sound waves originating within the chamber, there being a perforation through said wall in the region of said reflective surface, and a vibratory plate closing said perforation, said plate possessing a low acoustic impedance for the frequency of said detonation sound waves, and being thereby closely acoustically coupled to the combustion chamber for said detonation wave frequency.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,811,771 Wieman June 23, 1931 2,040,652 Gaty May 12, 1936 2,220,558 Van Dijck et a1. Nov. 5, 1940 2,297,046 Bourne Sept. 29, 1942 2,394,792 MacMillan Feb. 12, 1946 

